共查询到14条相似文献,搜索用时 7 毫秒
1.
一种采用压扩算法来降低OFDM信号PAPR的新方法 总被引:1,自引:1,他引:0
OFDM技术具有很高峰平功率比(PAPR),这是其实用化的一个瓶颈。针对这一问题,构造了一个新的压扩函数来降低OFDM信号的峰平功率比,通过计算机仿真表明,它不但可以大幅度降低OFDM信号的PAPR,而且,还可以通过适当的选择压扩系数得到一定的系统增益。 相似文献
2.
Shiann‐Shiun Jeng Jia‐Ming Chen Po‐Hao Chang 《International Journal of Communication Systems》2011,24(11):1467-1479
Orthogonal Frequency Division Multiplexing (OFDM) systems have become the most promising wireless communication systems in the recent years. For OFDM systems, there is one major drawback, which is the high peak‐to‐average power ratio (PAPR). Companding techniques have been frequently proposed to reduce PAPR. Exponential companding technique offers efficient PAPR reduction with a low bit error rate (BER). However, the exponential companding technique is difficult to implement. This paper utilizes the Padé approximation to simplify the exponential companding technique. The simulation results demonstrate that the proposed companding technique offers the same performance results as those of the exponential companding technique, while Additive White Gaussian Noise (AWGN) or multipath fading channel is considered. Further, the hardware implementation results show that the complexity of the proposed companding technique is less than that of the exponential companding technique. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
3.
PAPR reduction for OFDM‐based visible light communication systems using proposed hybrid technique
下载免费PDF全文
![点击此处可从《International Journal of Communication Systems》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Haitham Freag Emad S. Hassan Sami A. El‐Dolil Moawad I. Dessouky 《International Journal of Communication Systems》2018,31(10)
Orthogonal Frequency Division Multiplexing (OFDM) is utilized with visible light communication (VLC) systems to decrease the impacts of inter‐symbol interference and to achieve communication with high speed of data transmission and huge bandwidth. In any case, the main problem in OFDM‐based VLC systems is high peak‐to‐average power ratios (PAPRs). This paper proposes a hybrid PAPR reduction technique based on signal transformation combined with clipping. The Hadamard transform is used in the proposed technique to reduce the PAPR without affecting the bit error rate (BER) of the VLC systems. The optimum clipping threshold at which the PAPR is reduced simultaneously with the improvement the BER of the VLC systems is also determined. The performance of the proposed system is assessed in terms of complementary cumulative distribution function and the BER. The obtained results demonstrate that the proposed procedure can simultaneously decrease the PAPR and achieve good BER performance compared to the OFDM‐based VLC system. 相似文献
4.
In this article, a multiuser single carrier frequency division multiple access (SC-FDMA) system is considered, based on which an adaptive subcarrier and bit allocation algorithm is investigated. The algorithm has been used to achieve a subcarrier mapping mode in this system, which combines the advantages of single- and multi-carrier transmissions, such as, low peak to average power ratio, orthogonality of signals of different users, and low complexity. Simulation results show that it has a similar performance as that of the adaptive allocation algorithm in the orthogonal frequency division multiple (OFDM) system and the proposed mapping mode has a performance gain over the two existing mapping modes at the link level. 相似文献
5.
6.
Heung‐Gyoon Ryu 《Wireless Communications and Mobile Computing》2011,11(1):46-52
Orthogonal frequency division multiplexing (OFDM) has been widely used in many kinds of communication systems. However, OFDM signal has serious problem of high peak‐to‐average‐power ratio (PAPR) due to so many sub‐carriers. So, OFDM signal has very wide dynamic range. Therefore, the bit error rate (BER) performance may be degraded because of the nonlinear devices like the high power amplifier (HPA). Even if the linearization and large back‐off are used to compensate for the HPA nonlinearity, the power efficiency of the HPA is still very low since the PAPR is very high. Therefore, the PAPR reduction of the OFDM signal before the linearization would be more reasonable to improve the power efficiency and nonlinear compensation at the same time. In this paper, we propose a new combined method of SPW (sub‐block phase weighting) for PAPR reduction and linearization technique for the improvement of the power efficiency and for the nonlinear compensation of HPA. An updated SPW method is proposed to use a novel weighting factor multiplication of the complementary sequence characteristic and PAPR threshold technique. From the simulation results, it can be confirmed that BER performance is significantly improved and out‐of‐band spectrum radiations are much mitigated. Power efficiency of HPA can be enhanced since we can set small IBO (input back‐off) due to the PAPR reduction. The proposed system shows about 3 and 1 dB performance improvement than the LCP (linearized constant peak‐power)‐OFDM and LCP‐OFDM plus SPW at BER = 10−4. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
7.
This contribution deals with the digital broadcasting of HDTV channels over the cable television (CATV) distribution system, using either single-carrier QAM or an orthogonal frequency division multiplex (OFDM) of many QAM carriers to represent an HDTV channel. Assuming that no error-correcting codes are used, we investigate two distinct cases: in the first case, a few HDTV channels are transmitted among many analog TV channels, whereas in the second case all transmitted channels are HDTV channels. We show that in the first case the transmit power of an HDTV channel can be substantially reduced (by about 10 dB or more) as compared to the transmit power of an analog TV channel, while still maintaining a satisfactory bit error rate (BER). In the second case, not only a considerable reduction of the total transmit power but also a reduction of amplifier cost and an increase of the number of TV channels can be achieved. Single-carrier QAM is found to perform slightly better (at most about 1 or 2 dB) than a multi-carrier QAM. 相似文献
8.
A multi-carrier simultaneous wireless information and power transfer (SWIPT) communication system including one base station (BS) and one user was investigated,where both uplink and downlink adopt orthogonal frequency division multiplexing (OFDM).In the downlink,the BS transmited information and power to the user simultaneously.In the uplink,the user transmited information to the BS by using the power harvested from the BS in the downlink.The weighted sum of the downlink and uplink achievable rates by jointly optimizing subcarrier allocation and power allocation of the uplink and downlink were aimed to maximized.An optimal algorithm to solve the joint resource allocation problem was proposed,which was based on the Lagrange duality method and the ellipsoid method.Finally,the result shows the performances of the proposed algorithm by computer simulations. 相似文献
9.
10.
In OFDM systems, time‐varying channels destroy orthogonality between subcarriers causing Inter‐Carrier Interference. To reduce this effect, a Kalman filter, as a benchmark, is used for channel estimation, based on comb‐type pilot arrangements of the OFDM system. An advantage of comb‐type pilot arrangements in channel estimation is the ability to track the variation of the channel caused by Doppler frequency. Kalman method has been proposed to estimate the channel frequency response (CFR) at the pilot locations, then CFR, at data subchannels, is obtained by means of interpolation between estimates at pilot locations. The low‐complexity Kalman method is introduced to reduce the complexity of the system while achieving the same BER/SNR. Different types of interpolations have been also compared such as Low‐pass, Spline‐cubic and Linear interpolation methods. The BER/SNR performance of BPSK modulation schemes are considered for time varying Rayleigh fading channels. Our results has shown that the low‐complexity Kalman estimation, used with the pilot arrangement and a suitable interpolation method, gives almost the same performance as that of the Kalman method specially for low SNR values and hence the effect of Doppler shift effect is controlled. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
11.
12.
利用训练帧进行OFDM系统同步的新算法 总被引:14,自引:0,他引:14
本文主要讨论了OFDM系统的定时和频率偏差估计算法,针对现有的ML(最大似然)算法定量不够精确,频偏估计范围过小的缺点,提出了一种新算法,该算法利用OFDM训练帧进行定时估计和频偏捕获,结合ML算法进行频率估计,仿真结果说明,新算法克服了ML算法的缺点,能精确定时并进行较大范围的频偏估计。 相似文献
13.
Confidentiality of information must be maintained when it is required to be transmitted over a communication channel or when it is stored in a computer for further information access. Establishing a highly reliable and secure means of wireless communication for the transfer of digital data (text, images, audio, and video) from source to destination is becoming a prime requirement in present‐day wireless communications. Security can be achieved at the network level as well as at the data level. Data‐level security is made through cryptographic techniques. This paper emphasizes data‐level security aspects in a wireless communication system for the secure transmission of images over an AWGN channel condition. Here, a crypto orthogonal frequency division multiplexing system (crypto‐OFDM system) is designed using Rubik's cube encryption algorithm scheme for secured transmission of images under the MATLAB environment. The quality of the image transmission is analyzed using peak signal to noise ratio (PSNR) and BER at different SNR conditions. The quality of the encryption algorithm was also tested with statistical metrics, which are the histogram, NPCR, UACI, entropy, correlation coefficient analysis, etc. The numerical results reveal that a DCT‐based crypto‐OFDM system with Rubik's cube algorithm show a better performance over earlier cryptosystems and also perform superior to the original/basic OFDM system. The statistical analysis tests prove that Rubik's cube algorithm is one of the most robust algorithms for security point of view and is easy to implement, as Rubik's cube algorithm makes use of natural characteristics of pixel values, which form the basis for designing the secret key . 相似文献